In 2007, the New Yorker published staff writer Raffi Khatchadourian's lengthy and nuanced profile of "American Al Qaeda" Adam Gadahn, the California-born death metal enthusiast who converted to Islam, moved to Pakistan, and rose to the leadership of Al Qaeda. What the magazine has never reported: Gadahn wrote back.

After Khatchadourian's story ran in January 2007, Gawker has learned, he received an email from someone purporting to be Gadahn, as well as a letter addressed to the New Yorker's Times Square headquarters. In between jihadist rants, the letter offered praise for Khatchadourian's account of Gadahn's youth and criticized his treatment of the young man's descent into militant Islam. It also challenged Khatchadourian on some details, claiming, contrary to Khatchadourian, that Gadahn never wore blue jeans.

Khatchadourian had no idea how seriously to take the letter. He wrote back to the email address, seeking verification, but got no response. "It might have been him," he told Gawker. "It seemed like him. But who knows? It could have been a hoax." The New Yorker's editors did, however, immediately contact the FBI, not least because the letter appeared to Khatchadourian to have been hand-delivered, rather than mailed—which meant an Al Qaeda messenger might have been traipsing through Times Square. (It turned out that it had been mailed from either Dubai or one of the Arab emirates, Khatchadourian recalls, but the outer envelope with postage had been discarded by a mail room employee.)

The New Yorker may have had its doubts, but the FBI took the letter very seriously, and at least one veteran counterterrorism agent became convinced that it was genuine. Gawker has obtained a private memo apparently written by Mark Rossini, a former supervisory special agent with the FBI who was working in the office of public affairs in 2007, describing the FBI's response to the Gadahn letter as "a highly complex investigation." (Rossini was a bureau veteran who had served as the FBI's representative to the CIA's Counterterrorism Center in the run-up to the 9/11 attacks. The memo is a defensive summary of Rossini's career at the FBI written after he was accused of illegally accessing a bureau investigative database, a crime to which he pleaded guilty in 2009. The memo was posted, along with several other documents concerning Rossini's career, on a password-protected web site promoted to a variety of reporters by an anonymous email correspondent last month.)

The memo, which alternates between first and third person references to Rossini, says the Gadahn letter sparked a major investigation "utilizing the most sensitive investigative techniques at the disposal" of the U.S. government (though the references to Gadahn and the New Yorker are partially redacted in the memo, it's obvious from context and some unobscured letters what they refer to):

SSA [supervisory special agent] Rossini worked on a highly sensitive matter when fugitive Adam Gadahn contacted the New Yorker magazine via email and parcel post. SSA Rossini was the first person in law enforcement that editor of the New Yorker (David Remnick) contacted. SSA Rossini responded that evening and worked through that night and subsequent days and weeks with FBI personnel in the Office of Public Affairs in Washington D.C. and New York as well as SA's [special agents] from the Coutnerterrorism Division in Los Angeles, New York and FBIHQ (LA since Gadahn was indicted there). SSA Rossini was the main conduit of the FBI with New Yorker personnel due to his experience, liaison skills and expertise on counterterrorism investigations and public affairs. SSA Rossini had to simultaneously maintain and promote cooperation with a world renowned periodical while facilitating a highly complex investigation utilizing the most sensitive investigative techniques at the disposal of the USG.

Khatchadourian says FBI agents took the brown wrapper the letter came in to analyze it for fingerprints, and followed up at least twice to ask if he had received any further correspondence. But they never indicated to him that the FBI was confident—at least as confident as Rossini's memo seems to indicate—that the writer was indeed a high-level Al Qaeda operative. The New Yorker never published or reported on the letter, he says, because it wasn't sure of its provenance. Asked to furnish a copy, he declined:

"I still have the letter, but I also have accumulated thousands of other documents since then, and I would have to hunt for it. In any case, we didn't publish the letter five years ago, and since we don't know exactly what it is we have, I don't see us releasing it now. If we did one day decide to use it for a story we would obviously do that here."

An FBI spokesman did not return an email seeking comment, and Rossini declined to speak for the record.